CQ/HCQ regulate the release of various pro-inflammatory factors, which are important immunomodulators. Intracellular alkalinization by CQ/HCQ inhibits lysosomal activity, preventing antigen processing, major histocompatibility complex (MHC) class II expression and immune activation [40]. This process can inhibit T cell activation and block expression of CD154 on the surface of CD4 + T cells [41]. CQ also reduces cytokines such as interleukin (IL)-1, IL-6 and tumor necrosis factor-α (TNF-α) produced by T cells and B cells [42]. At the same time, changes of endosomal pH can interfere with Toll-like receptor (TLR) signaling, such as TLR7 and TLR9 processing, inhibiting the activation and production of cytokines [43]. CQ/HCQ also weaken the cyclic GMP-AMP (cGAMP) synthase (cGAS) activity by inhibiting cytosolic DNA, thereby reducing type I interferon production [44]. In vitro, CQ/HCQ can also inhibit phospholipase A2, altering the metabolism of arachidonic acid, and reducing the production of prostaglandins [45]. Some clinical studies have found that high concentrations of cytokines and pro-inflammatory factors such as IL-6 and IL-10 are elevated in the plasma of critically ill patients infected with SARS-CoV-2 [46,47], suggesting that cytokine release syndrome (CRS) is associated with disease severity. In the aspect of immune response, HCQ/CQ therefore are likely to inhibit CRS, delaying the progression of COVID-19 (Figure 1).